1. Field of the Invention
The present invention relates a technique for discriminating the existence of communication paths in a lattice communication network control system and, more particularly, to a technique for reducing the computational complexity of communication path discriminating functions to determine a connection and disconnection between an overall network and its components, in a lattice communication network control system.
2. Description of the Related Art
In a lattice communication network system, main nodes are composed of lattice networks and connected to their extended nodes, that is, subnodes. Exemplars of recent design efforts for communication network systems include U.S. Pat. No. 5,604,868 to Komine et al., entitled Communication System Using Establishing Network Route, U.S. Pat. No. 5,636,203 to Shah, entitled Method And System For Identifying Fault Location In A Communications Network, U.S. Pat. No. 5,241,533 to Kimoto et al., entitled Packet Switching Network With Alternate Trunking Function, U.S. Pat. No. 4,797,882 to Maxemchuk, entitled Mesh-Based Switching Network, U.S. Pat. No. 5,581,543 to Natarajan, entitled Communication Network And Method Which Respond To A Failed Link, U.S. Pat. No. 5,495,471 to Chow et al., entitled System And Method For Restoring A Telecommunications Network Based On A Two Prong Approach, U.S. Pat. No. 5,463,615 to Steinhom, entitled Node Failure Restoration Tool, U.S. Pat. No. 5,173,689 to Kusano, entitled Self-Distributed Logical Channel Node Failure Restoring System, U.S. Pat. No. 5,548,639 to Ogura et al., entitled Distributed Control Of Telecommunication Network For Setting Up An Alternative Communication Path, U.S. Pat. No. 5,267,238 to Yano etal., entitled Network Interface Units And Communication System Using Network Interface Unit, and U.S. Pat. No. 5,315,593 to Adachi et al., entitled Communication Control Unit.
It has been customary to have the main nodes composed of lattice networks and connected to their extended nodes, that is, subnodes. When any status variation exists in each node such as a normal, abnormal, failure or unconfirmable state, the node reports its status variation to a management node. If the node cannot report its status due to a problem, the node's status is checked through the links connected to the node. Assuming that a main node has a fault, the management node receives a report that there is a problem in the links from the nodes connected to the main node. Since the problem may exist in the links connected to the main node having a fault, the management node sets the node not in a failure state but in an unconfirmable state.
When a problem is found in a main node with a fault in some of the links such that there is no communication path between the subnodes of the main node and the management node, the management node cannot receive a report that two of the links have a fault with a problem in one of the two terminal nodes of the link, and the two terminal nodes are both in a failure state. In such a case, the links connected to the main node and more undesirably, the main node remain in a normal state. The communication network control system is thus required to have a function to recognize the above problem by itself. With a fault in a link, the link is set in a failure state and it is determined whether paths exist from the two terminal nodes of the link and all of the nodes connected thereto to the management node. If there is a path, the status of the node is not changed. Otherwise the node and all links connected thereto are set in an unconfirmable state. Undesirably, the computational complexity increases according to the number of nodes connected to two terminal nodes and the construction of the links from a target node to the management node.